They were scored on a number of personality traits typical in psychopaths, including fearlessness, cold-heartedness and egocentricity.

While the study found Donald Trump's score puts him in the company of some of history's greatest despots, including Hitler and Ugandan dictator Idi Amin, his opponent Hillary Clinton found herself alongside Napoleon Bonaparte and Emperor Nero.

Mr Trump outstripped Hitler on factors including social influence and fearlessness, while the genocidal Nazi dictator scored higher on "Machiavellian egocentricity" and cold-heartedness.